In communication circuitry such as smartphones and tablets, powerful application processors are capable of providing high MIPS (Millions of Instructions Per Second) and utilizing high-frequency clocks.
Modern processors are relatively efficient and can operate at high MIPS/milliamp. However, operating at high MIPS results in large currents being drawn from a battery. For example, some games require operation at high MIPS. Other applications may also result in large currents, such as a vibrating alarm being triggered, or operating in a video mode.
These large currents result in a significant voltage drop of the battery voltage, due to the ESR (equivalent series resistance) of the battery and the battery connector. Battery voltage drops on the order of 1 volt may occur over very quickly, perhaps in one second or less. For example, a battery voltage may drop from 3.5 volts down to 2.5 volts. These battery voltage fluctuations are dynamic.
The battery voltage is conventionally used by bias circuitry to generate bias voltages for the power amplifiers. However, conventional bias circuitry requires a minimum bias supply voltage such as 3.2 volts to properly generate bias voltages. As a specific example, bias control circuitry located inside a CMOS (Complementary Metal Oxide Semiconductor) controller in a multimode multiband power amplifier requires a supply voltage of at least 3.2 volts in order to operate with enough headroom to provide proper bias voltage for power amplifiers.
Thus, if the battery voltage drops from 3.5 volts down to 2.5 volts (below 3.2 volts), then conventional bias circuitry may not operate properly, and the power amplifiers may not operate properly. This is a large problem.